078  
FXUS02 KWBC 121601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1059 AM EST MON FEB 12 2018  
 
VALID 12Z THU FEB 15 2018 - 12Z MON FEB 19 2018  
   
..OVERVIEW
 
 
EXPECT A CONTINUATION OF THE LONG TERM MEAN PATTERN FEATURING EAST  
PACIFIC RIDGING, A TROUGH EXTENDING INTO THE WESTERN U.S. FROM AN  
UPPER LOW JUST NORTH OF HUDSON BAY, AND A RIDGE OFF THE  
GULF/SOUTHEAST COASTS. WITHIN THIS PATTERN THE PRIMARY FEATURES  
OF INTEREST WILL BE EJECTING WESTERN U.S./SOUTHERN CANADA ENERGY  
THAT WILL SUPPORT PROGRESSION OF A FRONT EXTENDING FROM THE GREAT  
LAKES INTO THE PLAINS AS OF EARLY THU FOLLOWED BY DEEPENING TROUGH  
ENERGY DIGGING INTO THE NORTHWEST NEXT WEEKEND.  
 
   
..GUIDANCE PREFERENCES
 
 
LATEST GUIDANCE IS SUFFICIENTLY SIMILAR IN PRINCIPLE TO ALLOW FOR  
AN OPERATIONAL MODEL BLEND (00Z-06Z GFS AND 00Z ECMWF/UKMET/CMC)  
FOR DAYS 3-5 THU-SAT FOLLOWED BY A MODEL/MEAN BLEND (GFS/ECMWF/CMC  
PLUS 06Z GEFS/00Z ECMWF MEANS) FOR DAYS 6-7 SUN-MON. THE  
RESULTING FORECAST MAINTAINS GOOD CONTINUITY WITH ONLY MINOR  
DETAIL ADJUSTMENTS.  
 
CONFIDENCE IS NOT PARTICULARLY GREAT IN RESOLVING SPECIFICS OF  
ENERGY EJECTING FROM THE WEST DURING THE FIRST HALF OF THE PERIOD  
GIVEN CURRENT SPREAD AND RUN TO RUN VARIABILITY IN EXACTLY HOW THE  
ENERGY IS DISTRIBUTED WITHIN THE OVERALL TROUGH AND PROGRESSIVE  
NATURE OF THE OVERALL FLOW. THIS PROGRESSION SUGGESTS THE SLOWER  
00Z UKMET/CMC MAY BE LESS PROBABLE SOLUTIONS BUT ARE WITHIN THE  
FULL ENSEMBLE SPREAD. OVER THE PAST 1-2 DAYS GFS/GEFS MEAN RUNS  
HAVE GENERALLY TRENDED SLOWER TOWARD THE ECMWF SCENARIO FOR LOW  
PRESSURE CROSSING NEW ENGLAND BY EARLY FRI WITH THEIR SOLUTIONS  
NOW FAIRLY CLOSE.  
 
RECENT GFS/GEFS TRENDS ARE IN THE MORE AMPLIFIED ECMWF/ECMWF MEAN  
DIRECTION FOR THE UPPER TROUGH THAT DIGS INTO THE NORTHWEST BY THE  
LATTER HALF OF THE PERIOD. HOWEVER OFF THE WEST COAST THE PAST  
COUPLE ECMWF RUNS ARE AMONG THE MORE AMPLIFIED SOLUTIONS RELATIVE  
TO THE FULL 00Z ENSEMBLE SPREAD. THIS SEEMS TO RECOMMEND SOME  
CAUTION IN GOING TOO AGGRESSIVELY TOWARD THE OPERATIONAL ECMWF  
SCENARIO, MAKING THE LATE PERIOD MODEL/ENSEMBLE MEAN BLEND THE  
MOST REASONABLE OPTION AT THIS TIME.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
MODEL/ENSEMBLE SOLUTIONS ARE TARGETING AN AREA FROM MO/AR  
NORTHEASTWARD INTO THE UPPER OH VALLEY/CENTRAL APPALACHIANS FOR  
HEAVY RAINFALL POTENTIAL DURING THU-THU NIGHT AND PERHAPS  
LINGERING INTO FRI WITH THE APPROACH OF THE WAVY FRONT PUSHING  
SOUTHEAST FROM A GREAT LAKES-CENTRAL PLAINS ORIENTATION AT THE  
START OF THU. OTHER LOCATIONS SHOULD SEE LIGHTER AMOUNTS FROM  
THIS FRONT. EXPECT A PERIOD OF DRIER WEATHER OVER THE EAST BEHIND  
THE FRONT BUT PRECIP WILL LIKELY EXPAND IN COVERAGE ONCE AGAIN BY  
SUN-MON AS HIGH PRESSURE MOVES OFF THE EAST COAST AND ANOTHER  
FRONT REACHES THE CENTRAL U.S. INITIAL WESTERN ENERGY ALOFT WILL  
GENERATE SOME SCATTERED SNOW IN THE ROCKIES (EXCEPT FOR RAIN IN  
SOUTHERN/LOW ELEVATION LOCATIONS) AT THE START OF THE PERIOD.  
THEN TROUGHING THAT DEEPENS OVER THE NORTHWEST WILL SPREAD SNOW  
AND LOW ELEVATION RAIN SOUTHWARD OVER THE NORTHERN HALF OF THE  
WEST WITH SNOW LEVELS DECREASING WITH TIME. HIGHEST AMOUNTS WITH  
THIS ACTIVITY WILL LIKELY BE OVER FAVORED TERRAIN NEAR THE COAST  
AND OVER THE CASCADES/NORTHERN ROCKIES.  
 
THE AMPLIFIED PATTERN WILL SUPPORT A WIDE RANGE OF TEMPERATURE  
EXTREMES IN THE THU-MON PERIOD. THE SOUTHERN HALF OF THE PLAINS  
AND MUCH OF THE EAST WILL SEE VERY WARM TEMPS LATE THIS WEEK AHEAD  
OF THE FIRST FRONT WITH SOME PLUS 20-30F ANOMALIES ESPECIALLY FOR  
MINS. AT THE SAME TIME VERY COLD AIR OVER THE NORTHERN PLAINS ON  
THU (20-30F BELOW NORMAL AT SOME LOCATIONS) WILL MODIFY SLIGHTLY  
AS IT PUSHES SOUTH/SOUTHEAST DURING THE REST OF THE WEEK. ANOTHER  
SURGE OF COLD AIR WITH READINGS AT LEAST AS LOW AS IN THE INITIAL  
ONE WILL LIKELY REACH THE NORTHERN PLAINS BY SUN-MON. AT THAT  
TIME MODERATELY ABOVE NORMAL TEMPS WILL RETURN OVER THE CENTRAL  
PLAINS AND THROUGH MOST OF THE EAST.  
 
RAUSCH  
 

 
 
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